Traditionally rigid endoscopes have a fixed viewing direction. Depending on the endoscope, the viewing direction can be either straight forward along the longitudinal axis of the scope, or it can be set at an angle to the longitudinal axis. A variety of off-angles are available depending on the application. For example, in sinoscopy typical scope angles can be 0, 30, 45, 70, and 90, while in cystoscopy the angles are typically 0, 30, 70, and 120. The endoscopist needs this range of angles in order to maximize the visual coverage of an internal structure. With only a straight forward viewing scope, the viewing range is severely limited. In large cavities, such as the abdomen, the operator can compensate for a fixed forward viewing angle by changing the entry angle of the laparoscope, and can thus with skilled manipulation increase the viewing range somewhat. However, in many cases, such as neuroendoscopy, sinoscopy, or otoscopy, the endoscope shaft is physically constrained or must remain largely stationary to avoid injuring the patient.
There are a number of drawbacks with using multiple endoscopes of different angles. Firstly, and most critically, inserting an off-angle endoscope can be dangerous because the operator can not see forward while the scope is being inserted. This problem is so severe that in neuroendoscopy for example, many surgeons will not use off-angle endoscopes because they are afraid of damaging delicate brain tissue. The result of this is regularly missed tumors growing outside the visual range. Similarly, in cystoscopy and certain types of laparoscopy, the surgeons are often concerned with using off-axis scopes for fear of injuring tissue ahead of or behind the viewing side of the scope. Secondly, each time a scope must be retracted and replaced with a scope of different a viewing angle, the operator can lose orientation and established visual reference points. Thirdly, repeated insertions and retractions are time consuming and annoying. Finally, the preparation, storage, and cleaning required for multiple endoscopes is impractical. There is also significant additional cost associated with having to supply multiple endoscopes for each procedure.
There have been a number of attempts to design variable direction of view endoscopes which can change their line of sight in situ and thus remove the need for multiple instruments. Examples of such devices are disclosed in U.S. Pat. No. 3,856,000 to Chikama, U.S. Pat. No. 6,371,909 to Hoeg, U.S. Pat. No. 6,560,013 to Ramsbottom, U.S. Pat. No. 4,697,577 to Forkner, U.S. Pat. No. 6,500,115 to Krattiger et al., and U.S. Pat. No. 5,762,603 to Thompson, which mechanically or electromechanically change the viewing direction, and in U.S. Pat. No. 5,313,306 to Kuban, and U.S. Pat. No. 5,800,341 to McKenna et al., which electronically change the viewing direction within a large captured field. These endoscopes can be disorienting and difficult to control. Hale et al. in U.S. Pat. No. 6,663,559 solve these control and orientation problems by computer-aided navigation. While effective, the advanced capabilities afforded by Hale et al. are not always necessary, especially when doing certain types of diagnoses. While the methods taught by Hale et al. appear to be the future direction of endoscopy, most surgeons for example, have been trained to use endoscopes with fixed viewing angles and are therefore sometimes reluctant to adopt new endoscopic viewing techniques. Specifically, many surgeons have come to rely on the specific viewpoints provided by fixed angle scopes. Rather than endoscopically navigating a cavity attempting to correlate the view with a preexisting knowledge of what the anatomy should look like, surgeons tend to associate a certain endoscopic viewing angle with a certain view and have developed mental links between viewing reference points and scope types. They have also become accustomed to correlating the position of structural features on the endoscope, such as the light post, with the orientation and direction of the endoscopic view. These established mental couplings between the endoscope configuration and the live image have become and important part of the endoscopic viewing process and are therefore difficult to reform.
Accordingly, the object of the present invention is to provide endoscopists with the advantages of traditional fixed-angle endoscopy while avoiding the disadvantages of using multiple instruments. Still further objects and advantages will become apparent from the ensuing description and drawings.